Load circuit for testing USB ports

ABSTRACT

An exemplary load circuit includes a switch unit and a current dividing circuit. The switch unit includes a number of switches. The current dividing circuit includes a number of sub-circuits. A terminal of a resistance module of each of the sub-circuits is connected to both a power terminal and a terminal of a corresponding one of the switches. The other terminal of the resistance module of each of the sub-circuits is connected to a drain of a transistor of each of the sub-circuits. A source of the transistor is connected to ground. A gate of the transistor is connected to ground, and is also connected to another terminal of the corresponding switch.

BACKGROUND

1. Technical Field

The disclosure generally relates to load circuits, and particularly to aload circuit for testing Universal Serial Bus (USB) ports.

2. Description of the Related Art

USB ports include four different kinds, namely type 1.0, type 1.1, type2.0, and type 3.0. For testing a performance of the various USB ports,many different standard load currents are needed. Typically, any oneload circuit used in such testing can only simulate one standard loadcurrent. As a result, different load circuits must be provided fordifferent kinds of USB ports, which is inconvenient and costly.

Therefore, there is room for improvement within the art.

BRIEF DESCRIPTION OF THE DRAWINGS

Many aspects of the present embodiments can be better understood withreference to the following drawings. The components in the drawings arenot necessarily drawn to scale, the emphasis instead being placed uponclearly illustrating the principles of the present embodiments.Moreover, in the drawings, like reference numerals designatecorresponding parts throughout the several diagrams. Wherever possible,the same reference numbers are used throughout the drawings to refer tothe same or like elements of an embodiment.

FIG. 1 is a circuit diagram of a load circuit used for testing USBports, according to an exemplary embodiment.

FIG. 2 is a circuit diagram of a first sub-circuit of the load circuitshown in FIG. 1, together with circuitry of the load circuit associatedwith the first sub-circuit.

FIG. 3 is a circuit diagram of a second sub-circuit of the load circuitshown in FIG. 1, together with circuitry of the load circuit associatedwith the second sub-circuit.

FIG. 4 is a circuit diagram of a third sub-circuit of the load circuitshown in FIG. 1, together with circuitry of the load circuit associatedwith the third sub-circuit.

FIG. 5 is a circuit diagram of a fourth sub-circuit of the load circuitshown in FIG. 1, together with circuitry of the load circuit associatedwith the fourth sub-circuit.

FIG. 6 is a circuit diagram of a fifth sub-circuit of the load circuitshown in FIG. 1, together with circuitry of the load circuit associatedwith the fifth sub-circuit.

FIG. 7 is a circuit diagram of a sixth sub-circuit of the load circuitshown in FIG. 1, together with circuitry of the load circuit associatedwith the sixth sub-circuit.

DETAILED DESCRIPTION

FIG. 1 is a circuit diagram of a load circuit 100, according to anexemplary embodiment. The load circuit 100 is configured for simulatingdifferent standard load currents for a USB port 200 when the USB port200 is under test, or for two USB ports 200 when the USB ports 200 areunder test. Each USB port 200 can be 1.0 type, 1.1 type, 2.0 type or 3.0type, and includes a power terminal 201. In FIG. 1, for simplicity, onlyone USB port 200 is illustrated. In this embodiment, the voltage valueprovided by the power terminal 210 is +5V (volts). The load circuit 100includes a switch unit 11 and a current dividing circuit 13.

The switch unit 11 is a toggle switch, and includes first to sixteenthterminals, which are separately labeled as S1-S16. In this embodiment,the first terminal 51 can be electronically connected to anddisconnected from the sixteenth terminal S16 by pushing a correspondingone of eight shift bars (not labeled) of the switch unit 11, therebyproviding a first switch SW1. The second terminal S2 can beelectronically connected to and disconnected from the fifteenth terminalS15 by pushing a corresponding one of the shift bars, thereby providinga second switch SW2. The third terminal S3 can be electronicallyconnected to and disconnected from the fourteenth terminal S14 bypushing a corresponding one of the shift bars, thereby providing a thirdswitch SW3. The fourth terminal S4 can be electronically connected toand disconnected from the thirteenth terminal S13 by pushing acorresponding one of the shift bars, thereby providing a fourth switchSW4. The fifth terminal S5 can be electronically connected to anddisconnected from the twelfth terminal S12 by pushing a correspondingone of the shift bars, thereby providing a fifth switch SW5. The sixthterminal S6 can be electronically connected to and disconnected from theeleventh terminal S11 by pushing a corresponding one of the shift bars,thereby providing a sixth switch SW6. The seventh terminal S7 can beelectronically connected to and disconnected from the tenth terminal S10by pushing a corresponding one of the shift bars, thereby providing aseventh switch SW7. The eighth terminal S8 can be electronicallyconnected to and disconnected from the ninth terminal S9 by pushing acorresponding one of the shift bars, thereby providing an eighth switchSW8. In this embodiment, the eighth switch SW8 is idle.

The current dividing circuit 13 includes a first sub-circuit 131, asecond sub-circuit 132, a third sub-circuit 133, a fourth sub-circuit134, a fifth sub-circuit 135, and a sixth sub-circuit 136.

Referring to FIG. 2, the first sub-circuit 131 includes a firstresistance module Rf1, a first transistor M1, and resistors R1, R2. Aterminal of the first resistance module Rf1 is connected to both thepower terminal 201 and a terminal of the first switch SW1 (e.g., thefirst terminal S1). The other terminal of the first resistance moduleRf1 is connected to a drain of the first transistor M1. A source of thefirst transistor M1 is connected to ground. A gate of the firsttransistor M1 is connected to ground via the resistor R1, and is alsoconnected to the other terminal of the first switch SW1 (e.g., thesixteenth terminal S16) through the resistor R2.

Referring to FIG. 3, the second sub-circuit 132 includes a secondresistance module Rf2, a second transistor M2, and resistors R3, R4. Aterminal of the second resistance module Rf2 is connected to both thepower terminal 201 and a terminal of the second switch SW2 (e.g., thesecond terminal S2). The other terminal of the second resistance moduleRf2 is connected to a drain of the second transistor M2. A source of thesecond transistor M2 is connected to ground. A gate of the secondtransistor M2 is connected to ground via the resistor R3, and is alsoconnected to the other terminal of the second switch SW2 (e.g., thefifteenth terminal S15) through the resistor R4.

Referring to FIG. 4, the third sub-circuit 133 includes a thirdresistance module Rf3, a third transistor M3, and resistors R5, R6. Aterminal of the third resistance module Rf3 is connected to both thepower terminal 201 and a terminal of the third switch SW3 (e.g., thethird terminal S3). The other terminal of the third resistance moduleRf3 is connected to a drain of the third transistor M3. A source of thethird transistor M3 is connected to ground. A gate of the thirdtransistor M3 is connected to ground via the resistor R5, and is alsoconnected to the other terminal of the third switch SW3 (e.g., thefourteenth terminal S14) through the resistor R6.

Referring to FIG. 5, the fourth sub-circuit 134 includes a fourthresistance module Rf4, a fourth transistor M4, and resistors R7, R8. Aterminal of the fourth resistance module Rf4 is connected to both thepower terminal 201 and a terminal of the fourth switch SW4 (e.g., thefourth terminal S4). The other terminal of the fourth resistance moduleRf4 is connected to a drain of the fourth transistor M4. A source of thefourth transistor M4 is connected to ground. A gate of the fourthtransistor M4 is connected to ground via the resistor R7, and is alsoconnected to the other terminal of the fourth switch SW4 (e.g., thethirteenth terminal S13) through the resistor R8.

Referring to FIG. 6, the fifth sub-circuit 135 includes a fifthresistance module Rf5, a fifth transistor M5, and resistors R9, R10. Aterminal of the fifth resistance module Rf5 is connected to both thepower terminal 201 and a terminal of the fifth switch SW5 (e.g., thefifth terminal S5). The other terminal of the fifth resistance moduleRf5 is connected to a drain of the fifth transistor M5. A source of thefifth transistor M5 is connected to ground. A gate of the fifthtransistor M5 is connected to ground via the resistor R9, and is alsoconnected to the other terminal of the fifth switch SW5 (e.g., thetwelfth terminal 12) through the resistor R10.

Referring to FIG. 7, the sixth sub-circuit 136 includes a sixthresistance module Rf6, a sixth transistor M6, and resistors R11, R12. Aterminal of the sixth resistance module Rf6 is connected to both thepower terminal 201 and a terminal of the sixth switch SW6 (e.g., thesixth terminal S6). The other terminal of the sixth resistance moduleRf6 is connected to a drain of the sixth transistor M6. A source of thesixth transistor M6 is connected to ground. A gate of the sixthtransistor M6 is connected to ground via the resistor R11, and is alsoconnected to the other terminal of the sixth switch SW6 (e.g., theeleventh terminal S11) through the resistor R12.

In this embodiment, the resistances of the first to sixth resistancemodules Rf1-Rf6 are respectively about 50 ohms, 50 ohms, 35 ohms, 35ohms, 10 ohms, and 7 and 1/7 ohms. In detail, the first resistancemodule Rf1 includes four resistors R13-R16 connected in series. Theresistances of the four resistors R13-R16 are respectively about 15ohms, 15 ohms, 10 ohms, and 10 ohms. The second resistance module Rf2includes four resistors R17-R20 connected in series. The resistances ofthe four resistors R17-R20 are respectively about 15 ohms, 15 ohms, 10ohms, and 10 ohms. The third resistance module Rf3 includes threeresistors R21-R23 connected in series. The resistances of the threeresistors R21-R23 are respectively about 10 ohms, 10 ohms, and 15 ohms.The fourth resistance module Rf4 includes three resistors R24-R26connected in series. The resistances of the three resistors R24-R26 arerespectively about 15 ohms, 10 ohms, and 10 ohms.

The fifth resistance module Rf5 includes four resistors R27-R30. Theresistors R27-R28 are connected in series, and the resistors R29-R30 areseparately connected in series. The two series of resistors, namely theresistors R27-R28 and the resistors R29-R30, are connected in parallelbetween the power terminal 201 and the drain of the fifth transistor M5.The resistances of the four resistors R27-R30 are all about 10 ohms. Thesixth resistance module Rf6 includes eight resistors R31-R38. Theresistors R31-R32 are connected in series, the resistors R33-R34 areseparately connected in series, the resistors R35-R36 are separatelyconnected in series, and the resistors R37-R38 are separately connectedin series. The four series of resistors, namely the resistors R31-R32,the resistors R33-R34, the resistors R35-R36 and the resistors R37-R38,are connected in parallel between the power terminal 201 and the drainof the sixth transistor M6. The resistances of the eight resistorsR31-R38 are respectively about 15 ohms, 10 ohms, 15 ohms, 10 ohms, 10ohms, 10 ohms, 10 ohms, and 10 ohms.

When the first switch SW1 is turned on and the other switches SW2-SW8are turned off, the power terminal 201 outputs a high level signal(e.g., logic 1) to the gate of the first transistor M1 through the firstswitch SW1, thereby driving the first transistor M1 to turn on. In thisway, a current I1 flowing through the first resistance module Rf1 andthe first transistor M1 is about

$\frac{Vcc}{{Rf}\; 1} = {\frac{5}{50} = {100\mspace{14mu}{{mA}.}}}$

Similarly, when the second switch SW2 is turned on and the otherswitches SW1 and SW3-SW8 are turned off, a current I2 flowing throughthe second resistance module Rf2 and the second transistor M2 is about100 mA (milliamperes). When the third switch SW3 is turned on and theother switches SW1-SW2 and SW4-SW8 are turned off, a current I3 flowingthrough the third resistance module Rf3 and the third transistor M3 isabout 150 mA. When the fourth switch SW4 is turned on and the otherswitches SW1-SW3 and SW5-SW8 are turned off, a current I4 flowingthrough the fourth resistance module Rf4 and the fourth transistor M4 isabout 150 mA. When the fifth switch SW5 is turned on and the otherswitches SW1-SW4 and SW6-SW8 are turned off, a current I5 flowingthrough the fifth resistance module Rf5 and the fifth transistor M5 isabout 500 mA. When the sixth switch SW6 is turned on and the otherswitches SW1-SW5 and SW7-SW8 are turned off, a current I6 flowingthrough the sixth resistance module Rf6 and the sixth transistor M6 isabout 900 mA.

Referring to the table below, when one type of the USB port 200 istested, a tester turns on one or a plurality of the first to sixthswitches SW1-SW6, thereby connecting one or a plurality of the first tosixth sub-circuits 131-136 to the USB port 200. For example, when thefirst switch SW1 or the second switch SW2 is turned on, the currentdividing circuit 13 consumes a load current of about 100 mA via thefirst sub-circuit 131 or the second sub-circuit 132 to simulate aminimum-standard load current for one USB port 200 of type 1.0, type1.1, or type 2.0. When the first switch SW1 and the second switch SW2are turned on, the current dividing circuit 13 consumes a load currentof about 200 mA via both the first sub-circuit 131 and the secondsub-circuit 132 to simulate a minimum-standard load current for two USBports 200 of type 1.0, type 1.1, or type 2.0. When the third switch SW3or the fourth switch SW4 is turned on, the current dividing circuit 13consumes a load current of about 150 mA via the third sub-circuit 133 orthe fourth sub-circuit 134 to simulate a minimum-standard load currentfor a USB port 200 of type 3.0. When the first to fourth switchesSW1-SW4 are turned on, the current dividing circuit 13 consumes a loadcurrent of about 1000 mA via the first to fourth sub-circuits 131-134 tosimulate a maximum-standard load current for two USB ports 200 of type1.0, type 1.1, or type 2.0.

The table below sets out a relation between states of the switches andload currents:

Load current (mA) (Imin: a minimum- standard load current; States of theswitches Imax: a maximum- (1: on; 0: off) Type Amount standard loadcurrent) SW1 SW2 SW3 SW4 SW5 SW6 type 1.0, one Imin 100 1 0 0 0 0 0 type1.1, 0 1 0 0 0 0 or type Imax 500 1 1 1 1 0 0 2.0 two Imin 200 1 1 0 0 00 Imax 1000 1 1 1 1 1 0 type 3.0 one Imin 150 0 0 1 0 0 0 0 0 0 1 0 0Imax 900 1 0 1 1 1 0 two Imin 300 0 0 1 1 0 0 Imax 1800 1 0 1 1 1 1

In use, when one type of the USB port 200 is tested, the tester turns onone or a plurality of the first to sixth switches SW1-SW6. In detail,when one USB port 200 of type 1.0, type 1.1, or type 2.0 is beingtested, the first sub-circuit 131 or the second sub-circuit 132 isconnected to the USB port 200 under test to consume a minimum-standardload current by means of turning on the first switch SW1 or the secondswitch SW2; and the first to fourth sub-circuits 131-134 are connectedto the USB port 200 under test to consume a maximum-standard loadcurrent by means of turning on the first to fourth switches SW1-SW4.When two USB ports 200 of type 1.0, type 1.1, or type 2.0 are beingtested, both the first sub-circuit 131 and the second sub-circuit 132are connected to the USB ports 200 under test to consume aminimum-standard load current; and the first to fifth sub-circuits131-135 are connected to the USB ports 200 under test to consume amaximum-standard load current.

When one USB port 200 of type 3.0 is being tested, the third sub-circuit133 is connected to the USB port 200 under test to consume aminimum-standard load current; and the first sub-circuit 131 and thethird to fifth sub-circuits 133-135 are all connected to the USB port200 under test to consume a maximum-standard load current. When two USBports 200 of type 3.0 are being tested, both the third sub-circuit 133and the fourth sub-circuit 134 are connected to the USB ports 200 undertest to consume a minimum-standard load current; and the firstsub-circuit 131 and the third to sixth sub-circuits 133-136 are allconnected to the USB ports 200 under test to consume a maximum-standardload current.

In other embodiments, the load circuit 100 further includes amalfunction indication circuit 15. The malfunction indication circuit 15includes a light-emitting diode (LED) D1. An anode of the LED D1 isconnected to the power terminal 201 through a resistor R39. A cathode ofthe LED D1 is connected to ground. When the power terminal 201 providesa normal voltage to the load circuit 100, the voltage is connected toground via the resistor R39 and the LED D1, and the LED D1 is turned on.When the power terminal 201 is unable to output any voltage due to amalfunction, the LED D1 is off, as an indication to the user.

In other embodiments, the load circuit 100 further includes afunction-testing circuit 17. The function-testing circuit 17 includes acontrol switch SW-PB. A terminal of the control switch SW-PB isconnected to the power terminal 201 via the seventh switch S7, and theother terminal of the control switch SW-PB is connected to ground. Theuser can test the short-circuit performance of the load circuit 100 whenthe seventh switch S7 and the control switch SW-PB are both turned on.

In the present specification and claims, the word “a” or “an” precedingan element does not exclude the presence of a plurality of suchelements. Further, the word “comprising” does not exclude the presenceof elements or steps other than those listed.

It is to be also understood that even though numerous characteristicsand advantages of exemplary embodiments have been set forth in theforegoing description, together with details of the structures andfunctions of the embodiments, the disclosure is illustrative only, andchanges may be made in detail, especially in matters of arrangement ofparts within the principles of this disclosure to the full extentindicated by the broad general meaning of the terms in which theappended claims are expressed.

What is claimed is:
 1. A load circuit for simulating different standardload currents for different kinds of Universal Serial Bus (USB) ports,each of the USB ports comprising a power terminal; the load circuitcomprising: a switch unit comprising a plurality of switches; and acurrent dividing circuit comprising a plurality of sub-circuits, each ofthe sub-circuits comprising a resistance module and a transistor,wherein a terminal of the resistance module of each of the sub-circuitsis connected to both the power terminal and a terminal of acorresponding one of the switches, another terminal of the resistancemodule of each of the sub-circuits is connected to a drain of thetransistor, a source of the transistor is connected to ground, and agate of the transistor is connected to ground through a resistor and isalso connected to another terminal of the corresponding switch throughanother resistor.
 2. The load circuit of claim 1, further comprising amalfunction indication circuit, wherein the malfunction indicationcircuit comprises a light-emitting diode (LED), an anode of the LED isconnected to the power terminal through a resistor, and a cathode of theLED is connected to ground.
 3. The load circuit of claim 1, wherein theswitch unit is a toggle switch, and comprises first to sixteenthterminals, the first terminal is electronically connectable to anddisconnectable from the sixteenth terminal to form a first switch, thesecond terminal is electronically connectable to and disconnectable fromthe fifteenth terminal to form a second switch, the third terminal iselectronically connectable to and disconnectable from the fourteenthterminal to form a third switch, the fourth terminal is electronicallyconnectable to and disconnectable from the thirteenth terminal to form afourth switch, the fifth terminal is electronically connectable to anddisconnectable from the twelfth terminal to form a fifth switch, thesixth terminal is electronically connectable to and disconnectable fromthe eleventh terminal to form a sixth switch, the seventh terminal iselectronically connectable to and disconnectable from the tenth terminalto form a seventh switch, and the eighth terminal is electronicallyconnectable to and disconnectable from the ninth terminal to form aneighth switch.
 4. The load circuit of claim 3, further comprising afunction-testing circuit, wherein the function-testing circuit comprisesa control switch, a terminal of the control switch is connected to thepower terminal via the seventh switch, and another terminal of thecontrol switch is connected to ground.
 5. The load circuit of claim 3,wherein the eighth switch is idle.
 6. The load circuit of claim 3,wherein the plurality of the sub-circuits comprises a first sub-circuitcorresponding to the first switch, a second sub-circuit corresponding tothe second switch, a third sub-circuit corresponding to the thirdswitch, a fourth sub-circuit corresponding to the fourth switch, a fifthsub-circuit corresponding to the fifth switch, and a sixth sub-circuitcorresponding to the sixth switch.
 7. The load circuit of claim 6,wherein the resistance of the resistance module of the first sub-circuitis about 50 ohms.
 8. The load circuit of claim 6, wherein the resistanceof the resistance module of the second sub-circuit is about 50 ohms. 9.The load circuit of claim 6, wherein the resistance of the resistancemodule of the third sub-circuit is about 35 ohms.
 10. The load circuitof claim 6, wherein the resistance of the resistance module of thefourth sub-circuit is about 35 ohms.
 11. The load circuit of claim 6,wherein the resistance of the resistance module of the fifth sub-circuitis about 10 ohms.
 12. The load circuit of claim 6, wherein theresistance of the resistance module of the sixth sub-circuit is about 7and 1/7 ohms.
 13. A load circuit, comprising: a switch unit comprising aplurality of switches; and a current dividing circuit comprising aplurality of sub-circuits; wherein each of the sub-circuits isconnectable to at least one Universal Serial Bus (USB) port andconnected to a corresponding one of the switches; each of thesub-circuits is configured to draw a respective load current from the atleast one USB port when the sub-circuit is connected to the at least oneUSB port and the corresponding switch is turned on; and when a selectedone or a selected plurality of the switches is or are turned on, thecorresponding one sub-circuit or corresponding plurality of sub-circuitsis or are connected to the at least one USB port, and the correspondingone sub-circuit or corresponding plurality of sub-circuits draw adesired load current from the at least one USB port.